This invention related to contact blades for use in electrical distribution systems and which are electromagnetically locked in closed position and, more particularly, to contact blades which are used for positively grounding high-voltage circuits for maintenance and repair operations.
After voltage has been removed from a high voltage circuit, ground blades are used to solidly ground the circuit, making it safe for maintenance, etc. The ground blades span the length of the circuit insulators when the blades are closed. Higher voltages require longer ground blades and consequently much higher operating forces. The high operating forces, especially under ice conditions of ground blades and side break disconnect switches, are often reduced by putting a folding joint in the blade near the disconnecting end of the blade to achieve a toggling or prying action. This folding or toggle blade makes opening extremely easy, which is a serious problem with long straight blades; however, it also makes it easy for electromagnetic forces, such as those generated by neighboring phases during short circuits, to "blow open" the blades, especially at high momentary ratings, even through the blades may be rigidly connected to a drive mechanism.